Surfactants or surface active agents are compounds which effect, usually in the form of reducing, surface tension between two phases usually when dissolved in water or water solutions. While soap is considered a surface active agent, the usual surfactant comprises an organic derivative such as a sodium salt of high molecular weight alkyl sulfates or sulfonates. The surfactants are used as detergents, wetting agents, penetrants, spreaders, dispersing agents or foaming agents. Therefore, such compounds find a wide variety of uses in many commercial applications. One such application is in enhanced oil recovery where after obtaining as much petroleum as possible due to natural sources such as pressure either by the petroleum itself or by the presence of gases, the residual petroleum still present in the reservoir is recovered by a secondary process. The secondary process usually involves forcing water into the reservoir to provide the pressure necessary to force the petroleum from the reservoir to the surface. However, at some point in the recovery of petroleum, a state is reached in which it is more costly to use the water pumped into the reservoir relative to the amount of oil which is recovered by this method. It is therefore necessary to effect the recovery of any petroleum which may still be present in the reservoir, either in a pool or by being trapped in interstices of relatively porous rock, by a tertiary method. One particular means for effecting the tertiary method is by utilizing surfactants as a plug, whereby the oil or petroleum which is present in the reservoir may be recovered by injecting an aqueous fluid containing a surfactant or a combination of surfactants along with other compounds into the reservoir. The use of surfactants in this system is necessary inasmuch as water alone does not displace the petroleum with a relatively high degree of efficiency. This occurs due to the fact that water and oil are relatively immiscible and, in addition, the interfacial tension between water and oil is relatively high. The use of surfactants will lower or reduce the interfacial tension between the water and the oil, thus reducing the force which retains the oil which has been trapped in capillaries, and will thus enable the oil to be recovered in a more efficient manner.
As will hereinafter be shown in greater detail, it has now been discovered that compounds which possess desirable surfactant properties may be prepared by utilizing, as one component thereof, the product resulting from the depolymerization of coal. Coal is basically a large cross-linked, complex natural polymer which can be depolymerized to yield simpler units. The depolymerization of coal may be effected by treating the coal with an organic solvent in the presence of certain catalysts to cleave the polymeric bonds in the coal structure and thus produce smaller molecules. The organic reagents or solvents which had been employed will comprise mono- or polyhydroxy aromatic compounds, while the catalysts which are employed will include Friedel Crafts catalysts as well as some acidic catalysts.
The depolymerization of the coal may be carried out by treating the coal at an elevated temperature in the presence of the organic solvent and the catalyst. After allowing the depolymerization reaction to continue for a predetermined period of time, the acid catalyst may then be neutralized by treatment with a basic compound such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, etc. The liquid and solids are separated by conventional means such as filtration, centrifugation, decantation, etc. The precipitates are then washed with organic solvents until a clear filtrate is obtained. The washings and decanted liquid are combined and subjected to distillation, preferably under reduced pressure, to yield a solid residue of depolymerized material. The depolymerized material may then be subjected to conventional refining processes to obtain the desired end product, which may then be used either per se or as components in further chemical reactions. The depolymerization of coal may be used as an alternative to other treatments of coal such as liquefaction which is usually accomplished by hydrogenation, solvent refining, etc.
It has now been discovered that the products which are obtained from the depolymerization of coal may be used directly, without any further process steps, to generate surfactants or surface active agents in a process which is hereinafter set forth in greater detail.